1. Field of the Invention
The present invention relates to a robot (manless car, self-movable robot, or car navigation system) movable along a predetermined path by itself, and more particularly to an apparatus for and a method of controlling driving of such a robot, capable of accurately moving the robot by correcting an output error of an angular velocity sensor adapted to detect a variation in travel direction of the robot.
2. Description of the Prior Art
Generally, a device for driving a movable robot includes an angular velocity sensor adapted to detect a variation in travel direction of the robot. However, such an angular velocity sensor involves an inherent output error. Such an inherent output error of the angular velocity sensor is generated every time when the travel direction of the robot is varied. The generated output errors are accumulated. Due to the accumulated output error, the robot may be difficult to direct in accordance with the user's intention (program).
For solving such a problem, there have been proposed various techniques of compensating the output error of angular velocity sensor. For example, Japanese Patent Laid-open Publication No. Heisei 04-238216 discloses a method for deriving a scale factor of a gyro. In accordance with this method, the robot provided with an angular velocity sensor for detecting a variation in travel direction is turned predetermined times at a fixed position, while the angular velocity sensor senses the turning angle of the robot for every turn of the robot. Turning angle data from the angular velocity sensor is accumulated so as to derive an output error of the angular velocity sensor by dividing the accumulated value by the actual turning angle of the robot. Based on the derived output error, the scale factor is adjusted.
In other words, as one of left and right wheels of the robot, for example, the right wheel is driven at a fixed state of the other wheel, that is, the left wheel, it turns about the left wheel along a circular track having a radius r corresponding to the distance between the left and right wheels. In this case, the actual turning angle can be calculated from the turning distance sensed by a travel distance sensor attached to the right wheel because the ratio of circumference of the circular track to its diameter is found. For example, where the travel distance is 2.pi.r, the actual turning angle is 360.degree. . The accumulated value of the turning angle data from the angular velocity sensor is divided by the calculated actual turning angle to derive the output error of the angular velocity sensor and thereby adjust the scale factor by the derived output error.
However, a slippage may occur at the driving wheel of the moving robot due to the material and condition of a bottom surface on which the robot travels. In the case of the above-mentioned conventional method, such a slippage is added as the travel distance even though the robot does not travel actually. As a result, the output error of the angular velocity sensor may be increased. This results in a difficulty to achieve an accurate control for driving of the robot.
The output error of the angular velocity sensor may be also increased due to a variation in surrounding conditions such as a surrounding temperature or a vibration. Although such an output error may be corrected using an absolute position display or an earth magnetic orientation sensor, this method involves problems of a complexity in construction and a long correction time.